1. Field of the invention
The present invention relates to diamond-coated articles characterized by superior adhesion of the diamond coating to the article serving as the substrate and to methods for fabricating such diamond-coated articles. More particularly, the present invention relates to articles coated with ultrasmooth diamond films and to fabrication methods for producing such articles.
2. The Prior Art
Diamond films typically exhibit grain-size growth that is proportional to the thickness of the film. Diamond grain size measured looking down at the top surface of the film is typically 10% of the film thicknesses. It is known to circumvent this behavior of thin membranes in diamond deposition processes by using cyclic renucleation, or simply by using high methane concentrations to cause continuous renucleation.
These known processes for forming small-grain-size films generally cannot be used successfully for films having thicknesses greater than a few microns (i.e., thicknesses greater than about ten microns). As nuclei grow during the deposition process, competitive interaction occurs between the nuclei causing the larger ones to get larger and the smaller ones to die out.
Small-grain-size films having thicknesses greater than are available using prior-art growth techniques could be extremely useful if applied to numerous applications, such as tooling inserts or other tools. The small grain size would provide a smooth film without the need to perform a polishing step subsequent to deposition. Such films could also enhance the ability to maintain sharp corners, increasing the value and applications of coated tools and other diamond film products.
In addition, one of the recurring problems in diamond coated tools is the delamination of the diamond coating from the substrate material due to the forces exerted on the tools in the machining environment. The problem of ensuring sufficient adhesion between the diamond film and the underlying substrate material has been a major stumbling block in the development of diamond coated tools.
It is therefore an object of the present invention to provide a small-grain-size diamond film having a thickness greater than is possible with prior art small-grain-size diamond films.
It is another object of the present invention to provide a process for growing a small-grain size diamond film to a thickness greater than is possible with prior art small-grain size diamond films.
It is yet another object of the present invention to provide a diamond coated tool comprising a tool substrate material coated with a small-grain-size diamond film having improved adhesion.